Optical information recording media for forming a recording medium on one side of a transparent substrate using light energy, and recording and reproducing using laser beams on the substrate side have been recently developed. Not only materials for a recording layer have been developed, but also protective films for preventing the recording layer from deteriorating due to moisture or oxygen have been developed (Japanese Laid-open Patent SHO. 59-68850/1984).
The protective layer is typically composed of a material having low moisture permeability, which may include, as inorganic matter, oxide films such as SiO.sub.2, MgO, Al.sub.2 O.sub.3. Examples of organic matter may be polypropylene, ethylene-vinyl acetate copolymer, and polyvinylidene chloride.
In an optical information recording medium, protection from moisture is explained below.
First, to prevent invasion of moisture through the substrate, oxides or fluorides are formed on the surface of the substrate. These inorganic materials are generally low in moisture permeability, and if the optical information recording medium is left in a high humidity atmosphere, corrosion of the recording medium may be prevented to a certain extent. Instead of these inorganic materials, similarly, by using organic high polymers relatively low in moisture permeability, such as polyvinylidene chloride, corrosion of the recording layer may be prevented. Moreover, as an organic high polymer protective film, crosslinking type resins such as epoxy resin are proposed (Japanese Laid-open Patent SHO. 57-70694/1982).
Such protective films, however, involve the following problems.
(1) Inorganic materials such as oxides and fluorides weakly adhere to the transparent substrate, and peeling or cracking may occur if left at a high temperature, high humidity condition.
(2) Oxides and fluorides do not readily form dense thin films.
(3) In organic high polymer materials, moisture barrier performance is limited although moisture permeability is low, and the moisture-proof effect is lost when stored for a long time under high temperature, high humidity conditions.
(4) When storing for a long time under high temperature, high humidity conditions, the crosslinking type resin is porous and is high in moisture permeability, and the recording layer is likely to deteriorate due to moisture.
Due to these reasons, when the optical information recording medium is stored under high temperature, high humidity conditions, the recording layer may corrode and deteriorate.
Instead of the conventional coating type magnetic recording medium, the magnetic recording medium forming a ferromagnetic metal thin film on a nonmagnetic support using a plating, sputtering, vacuum deposition, or ion plating method is being presently studied for use as a high density magnetic recording medium.
However, the magnetic recording medium using the ferromagnetic metal thin film fabricated in the above methods has its problems in wear resistance and running performance. That is, in the recording and reproducing process of a magnetic signal, the magnetic recording medium is set in a state of high speed relative motion against the magnetic head. At this time, running of the magnetic recording medium must be smooth and stable.
The ferromagnetic metal thin film fabricated in such methods, however, cannot withstand the rugged conditions in the process of magnetic recording or reproduction, and running becomes unstable due to wear of the magnetic head. Output may be significantly lowered in the course of running for a long time due to wear, tear or worn chips. It is accordingly proposed to form a monomolecular film composed of saturated fatty acid or its metal salt on the ferromagnetic metal thin film (Japanese Laid-open Patent SHO. 50-75001/1975).
In this case, although the initial lubricity is somewhat improved, the lubricity is not durable, and running stability and wear resistance are not sufficient. This is because the bonding of the monomolecular film of the saturated fatty acid and the ferromagnetic metal thin film is relatively weak, since the bonding is by physical adsorption, and the saturated fatty acid is shaved off by the sliding magnetic head or the like during running. To improve this point, it is known to form a protective film by coating the surface of the magnetic recording layer with a silane chemical adsorption film (U.S. Pat. No. 4,992,300).
In this known art, however, since the chemical adsorption film is formed by a liquid phase method using a chemical solvent, the substrate may be dissolved or swollen depending on the type of solvent. Another problem is peeling of the recording layer. Moreover, due to dust or contamination in the solvent, pin holes are likely to occur.